The present invention relates to attitude sensing as found in both the fields of inertial and satellite navigation systems. Satellite navigation receivers are known in which the signals from one or more navigation satellites are received and processed to provide attitude information. Interferometric techniques are utilized with a plurality of antennas to sense vehicle attitude relative to some base or inertial references. The receivers which track the satellite navigation signals are capable of extremely high attitude accuracy after they stabilize. Thereafter, their accuracy continues at a high level for indefinite periods. Such attitude information is important in space craft or surveying applications where pointing directions of high accuracy are necessary. In conditions of rapid vehicle maneuvering, the interferometric data changes too rapidly to be tracked by such navigation receivers and therefor attitude information is temporarily lost until the receiver can restabilize itself.
Inertial measurement units, typically consisting of three gyroscopes to detect rotation about three mutually orthogonal axes, as well as accelerometers to detect acceleration upon three mutually independent axes are known. Such units find applications in on board instrumentation such as for space vehicles and commercial aircraft. Inertial measurement units are capable of following with accuracy vehicle maneuverings at substantial rates. The inertial sensors of such inertial measurement units, however, are subject to error drift rates which, over time, contribute significant inaccuracies to the output indications of attitude.